The present resubmission application will address the urgent need for a more effective treatment approach for the 25% of substance use disordered (SUD) patients who have co-occurring posttraumatic stress disorder (PTSD). The gold standard treatment for PTSD in psychiatry is Prolonged Exposure, which uses a cognitive- behavioral approach that repeatedly and systematically exposes patients to memories of their traumatic events to reduce fear and arousal. Prolonged Exposure has only rarely been offered to SUD patients, in part due to concern that the intensive treatment will provoke increased drug use. In the handful of demonstration studies of exposure-based therapy for SUD patients, the primary limitation to its efficacy is poor adherence, rather than increased drug use. As many as 75% of SUD patients fail to complete the prescribed course of Prolonged Exposure sessions, which dramatically limits its effectiveness for SUD patients. Poor adherence to specialized psychiatric and other medical services in SUD populations is a common problem, and decades of substance abuse research have established that voucher-based contingency management approaches are highly effective in increasing low base-rate healthy behaviors in substance users. In this Stage Ib treatment development study, 62 male and female opioid-dependent and methadone treated patients with co-occurring current PTSD will be offered Prolonged Exposure therapy. Half of the sample will be randomly assigned to a Reinforced Prolonged Exposure condition that provides monetary-based incentives for attending the therapy sessions. The comparison condition will be assigned to a Standard Prolonged Exposure condition without the attendance incentives intervention. Groups will be compared primarily on adherence to the Prolonged Exposure therapy schedule, improvement in PTSD symptoms, and rates of drug use (urine specimens, self- reported use). The potential for increased drug use in particular, as well as other adverse events, will be proactively monitored and clinically managed throughout the treatment episode. The primary aims of the study are: Aim 1 - Evaluate the efficacy of adding voucher-based attendance incentives to Prolonged Exposure for PTSD to increase adherence in SUD patients in a methadone treatment program. Aim 2 - Evaluate the efficacy of adding voucher-based attendance incentives to Prolonged Exposure for PTSD to reduce PTSD symptoms in SUD patients. Aim 3 - Evaluate the effect of Prolonged Exposure for PTSD on rates of drug use in SUD patients. This study bridges two independent and important clinical achievements in psychiatric and substance abuse treatment to improve outcomes for SUD patients with co-occuring PTSD. This will also be the first known study to join the two evidence-based interventions of contingency management and the highly effective but poorly attended Prolonged Exposure for PTSD treatment. The potential impact of this work on research and clinical practice is considerable and far-reaching if, as anticipated, greater attendance to Prolonged Exposure reduces PTSD symptoms in SUD patients without increasing drug use.